Optical recording disk and production process therefor

ABSTRACT

An optical recording disk includes a light transmissive substrate, a recording film disposed on the substrate directly or through an intermediate layer and a protection film disposed on the recording film. The protection film consists of a dielectric material and the entirety of an upper flat surface and a side surface of the recording film is integrally covered with the dielectric material protection film.

BACKGROUND OF THE INVENTION

The present invention relates to an optical recording disk, and moreparticularly to an optical recording disk comprising a lighttransmissive substrate, a recording film disposed on the substratedirectly or through an intermediate layer, and a protection layerdisposed on the recording film, and a process for producing such anoptical recording disk.

Hitherto, there has been known, e.g., a photomagnetic disk (ormagnetoptical disk) as shown in FIG. 4 as one type of optical recordingdisk. More specifically in FIG. 4, a dielectric material film 52 isdisposed on a substrate 51 in the form of a disk, a recording film 53comprising a metal is disposed on the dielectric material film 52 and aprotection film 54 comprising a dielectric material is disposed on therecording film 53. Further, a protection plate 58 is bonded to theprotection film 54, generally through an adhesive layer 55. In addition,an outer peripheral side face of such a photomagnetic disk is filledwith a filler material 57 such as resin for the purpose of protectingthe recording film 53, particularly the side face thereof.

In the conventional photomagnetic disk as described above, the thinfilms are particularly produced according to a process as shown in FIGS.5 and 6. More specifically as shown in FIG. 5, a mask 80 in the form ofa ring is first disposed on a peripheral edge of the substrate 51 in theform of a disk which is fixed to a substrate holder 60 disposed in abell jar (not shown) of a vacuum film formation device. An innerperipheral face 80a of the mask 80 is disposed substantially in parallelwith a center line of the mask. After the mask 80 is disposed, thedielectric material film 52, the recording film 53 and the protectionfilm 54 are laminated on the substrate 51 by a vacuum film formation (orvacuum vapor deposition) process such as sputtering, as shown in FIG. 6.Then, the mask 80 is removed and the protection plate 58 is bonded tothe resultant product through the adhesive layer 55, and then the outerperipheral face of the resultant optical recording disk is filled withthe filler material 57 as shown in FIG. 4.

In the structure of the above conventional optical recording disk,however, the outer peripheral face of the recording film is exposed oris only covered with a filler comprising an organic material, even ifthe outer peripheral face is covered. As a result, it is not sufficientto prevent the corrosion of the recording film. Accordingly, there isposed a problem such that when the optical recording disk is leftstanding for a long period of time, the recording film of the opticalrecording disk begins to be corroded from the outer peripheral portionthereof, whereby the safety or reliability of the resultant productcannot be guaranteed.

SUMMARY OF THE INVENTION

A principal object of the present invention is to solve the aboveproblems and to provide an optical recording disk which is capable ofsolving the above problems and has a structure being excellent in thecorrosion resistance of the recording film, and a process for producingsuch an optical recording disk.

According to the present invention, there is provided an opticalrecording disk comprising a light transmissive substrate, a recordingfilm disposed on the substrate directly or through an intermediate layerand a protection film disposed on the recording film, wherein theprotection film consists of a dielectric material, and the entirety ofan upper flat surface and a side surface of the recording film isintegrally covered with the dielectric material protection film.

The present invention also provides a process for producing an opticalrecording disk, comprising the steps of:

disposing, on a peripheral edge portion of a disk substrate, a mask inthe form of a ring which has a projection portion over the entirety ofthe inner peripheral portion of the ring;

forming a recording film on the substrate by use of a sputteringprocess; and

forming a dielectric material protection film by use of a sputteringprocess under a working pressure which is higher than that used at thetime of the formation of the recording film.

In the recording film of the optical recording disk according to thepresent invention, the upper flat surface and the entirety of the sidesurface thereof is integrally covered with the dielectric materialprotection film, and therefore the corrosion thereof which isparticularly liable to occur in the side face (outer peripheral face)thereof can be prevented and the durability of the disk is improved.

In the process for producing an optical recording disk according to thepresent invention, there is used the mask in the form of a ring whichhas a projection portion along the entire periphery of the innerperipheral surface, and the dielectric material protection film isformed under a pressure of an inert gas which is higher than that usedat the time of the formation of the recording film, whereby the sideedge portion of the recording film is covered with the dielectricmaterial protection film.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a schematic sectional view of a photomagnetic recording diskaccording to the present invention, wherein a portion thereof is cutaway so that the peripheral portion can be observed;

FIG. 2 is a schematic sectional view for illustrating a process forproducing the photomagnetic recording disk according to the presentinvention, wherein a portion thereof is cut away so that the peripheralportion of the substrate can be observed, and wherein a mask is disposedon the substrate;

FIG. 3 is a schematic sectional view for illustrating a process forproducing the photomagnetic recording disk according to the presentinvention, wherein a portion thereof is cut away so that the peripheralportion of the substrate can be observed, and wherein a mask is disposedon the substrate and then a thin film is formed by sputtering;

FIG. 4 is a schematic sectional view of a photomagnetic recording diskproduced in the prior art, wherein a portion thereof is cut away so thatthe peripheral portion can be observed;

FIG. 5 is a schematic sectional view for illustrating a process forproducing the photomagnetic recording disk in the prior art, wherein aportion thereof is cut away so that the peripheral portion of thesubstrate can be observed, and wherein a mask is disposed on thesubstrate; and

FIG. 6 is a schematic sectional view for illustrating a process forproducing the photomagnetic recording disk in the prior aft, wherein aportion thereof is cut away so that the peripheral portion Of thesubstrate can be observed, and wherein a mask is disposed on thesubstrate and then a thin film is formed by sputtering.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow, there will be described a photomagnetic recording disk asan example of the optical recording disk according to the presentinvention.

FIG. 1 is a schematic sectional view of a photomagnetic recording disk 1according to the present invention, wherein a portion thereof is cutaway so that the peripheral portion thereof can be observed.

More specifically, the photomagnetic recording disk 1 comprises asubstrate 11 in the form of a disk, a dielectric material film 12 as anintermediate layer disposed on the substrate 11, a recording film 13disposed on the dielectric material film 12, and a protection film 14consisting of dielectric material disposed on the recording film 13. Ingeneral, a protection plate 18 is bonded to the protection film 14through an adhesive layer 15. In addition, an outer peripheral side faceof such a photomagnetic recording disk may preferably be filled with afiller material 17 such as resin for the purpose of protecting therecording film 13, particularly the side face thereof.

The substrate 11 in the form a disk may comprise a light transmissiveglass or resin such as polycarbonate (PC) and polymethylmethacrylate(PMMA). Such a substrate 11 may generally have a thickness of about 0.5to 1.5 mm.

The dielectric material film 12 to be disposed on the substrate 11 maycomprise a dielectric material such as ZnS, SiO, SiO₂, SiN_(x) (siliconnitride) AlN, AlON and CaF₂. Such a dielectric material film 12 maygenerally have a thickness of about 50 to 150 nm. The dielectricmaterial film 12 may be laminated on the substrate 11 so that aperipheral edge flat surface 11a of the substrate 11 remains, i.e., theedge flat surface 11a is not covered with the dielectric material film12.

The recording film 13 to be disposed on such a dielectric material film12 may comprise a film comprising a metal, particularly a photomagneticrecording material such as TbFeCo, GdTbFe, GaTbCo, GdFeBi, DyFe, GdFe,GdCo, BiSmYbCoGeIG, BiSmErGaIG, GdIG, CoCr, CrO₂, PtCo, EuOFe, EuO,MnCuBi, MnAlGe, MnBi and the like. Such a recording film 13 maygenerally have a thickness of about 15 to 100 nm. The recording film 13may be laminated on the substrate 11 so that the peripheral edge flatsurface 11a of the substrate 11 remains, i.e., the edge flat surface 11ais not covered with the recording film 13 similarly as in the case ofthe dielectric material film 12 as described above. Another material forthe recording film usable in the present invention may comprise any ofvarious known metal materials which are capable of being subjected tooptical recording. Specific examples of such a material may includerecording materials of a type which is capable of forming a pit, such asTe type, and recording materials of a type which is capable of causing aphase change such as As-Te-Ge type Sn-Te-Se type TeO_(x) type and Sb₂Se₃.

The recording film 13 may generally have a thickness of about 15 to 100nm. It is preferred that an outer peripheral edge portion of such arecording film 13 covers an outer peripheral edge portion 12a of thedielectric material film 12.

The protection film 14 is disposed on the recording film 13. As shown inthe drawing, such a protection film 14 is formed so that it integrallycovers not only an upper flat surface 13b of the recording film but alsothe entire surface of a side face 13a thereof. When the protection film14 is formed in such a manner, the side face of the recording film 13 isprevented from being corroded. Such a protection film 14 may be formedby using a dielectric material such as ZnS, SiO, SiO₂, SiN_(x) (siliconnitride), AlN, AlON and CaF₂, and the thickness thereof may generally beabout 50 to 100 nm. As described above, the protection plate 18 isbonded to the protection film 14 through the adhesive layer 15, asdescribed hereinabove. The adhesive layer 15 may comprise a materialsuch as ultraviolet ray curing (or hardening) resin, hot melt resin anddouble side coating tape, and the protection plate 18 may comprise amaterial such as glass, PC (poly carbonate), and PMMA(polymethylmethacrylate). In a further preferred embodiment, the outerperipheral side face of the optical recording disk is filled with afiller material 17.

Next, there will be described a process for producing the photomagneticrecording disk according to the present invention as described above,with reference to FIGS. 2 and 3. A sputtering process may be used as avacuum film formation (or vacuum vapor deposition) process.

First of all, the substrate 11 in the form of a disk is fixed to asubstrate holder 20 disposed in a bell jar (not shown) of a vacuum filmformation device. Then, a mask 30 in the form of a ring is disposed onthe peripheral edge of the substrate 11 in the form of a disk. The mask30 is characterized by the configuration or shape of the innerperipheral surface of the mask 30.

More specifically, the inner peripheral surface of the mask 30 has aprojection portion 30a having an inclined surface 32 projecting to theinside of the mask with respect to the surface 31 on which the mask isdisposed, and having an inclined surface 33 extending toward the outsidefrom the innermost portion of the projection portion 30a. The projectionportion 30a is formed along the entirety of the inner periphery of themask 30. The inclined surface 32 of the projection portion 30a mayincline at an angle of 10 to 60 degrees, more preferably 35 to 55degrees with respect to the surface 31 on which the mask 30 is disposed.When such an inclined surface 32 of the projection portion 30a provided,the material for the film to be formed may appropriately spread alongthe inclined surface 32, so that it may cover the side edge portion 13aof the recording film 13 as described above.

After the mask 30 is disposed on the substrate 11, the dielectricmaterial film 12 is caused to be laminated thereon in a manner ofsputtering by using a dielectric material as a target. In such a case,it is preferred that the outer peripheral edge face of the dielectricmaterial film 12 is caused to have a shape or configuration as shown inFIG. 3, which is formed so as not to occur the wraparound phenomena. Forthis reason, the pressure of an inert gas (i.e., pressure forsputtering) as a sputtering condition may preferably be 0.5 Pa or below,particularly preferably 0.02 to 0.2 Pa. Specific examples of the inertgas may include argon, helium, krypton, etc. . . . In general, argon maybe used in view of an economical factor.

Then, the recording film 13 is formed on the thus formed dielectricmaterial film 12 by using a sputtering process. In such a case, it ispreferred that the outer peripheral edge face of the recording film 13is formed so as to have a shape or configuration as shown in FIG. 3 byoccurring wraparound phenomenon slightly. For this reason, the pressureof an inert gas (e.g., pressure of the argon gas) as a sputteringcondition may preferably be higher than that used at the time of thefilm formation of the above dielectric material film 12. Morespecifically, the pressure of the inert gas may preferably beapproximately 0.2 to 0.6 Pa.

Then, the protection film 14 is formed on the thus formed recording film13 by using a sputtering process. In such a case, the pressure of aninert gas (e.g., pressure of the argon gas) as a sputtering conditionmay preferably be higher than that used at the time of the filmformation of the above recording film 13. At this time, the film formingmaterial for the protection film 14 spreads along the inclined surface32 of the projection portion 30a of the mask 30 so that it covers theside edge portion 13a of the above recording film 13. When the side edgeportion 13a is covered in such a manner, the resultant corrosionresistance may considerably be improved. More specifically, the pressureof the inert gas may preferably be 0.6 to 2 Pa, more preferably 0.8 to1.3 Pa.

When the above three species of the films are formed, the followingconditions may for example be used as the sputtering conditions:

Electric Power: 0.2 to 1.5 KW,

Target Voltage: 0.2 to 1.0 KV,

Target Interval: 50 to 200 mm,

Target Diameter: 100 to 300 mm, and

Substrate Temperature: 20° to 100° C.

After such a sputtering film formation process is completed, theresultant product comprising the substrate and the predetermined filmsformed thereon is taken out from the bell jar. Thereafter, the mask 30is removed from the resultant product, the protection plate 18 is bondedthereto through the adhesive layer 15, and the outer peripheral sideface of the resultant optical recording disk is filled with the fillermaterial 17.

Hereinbelow, the present invention is described in further detail withreference to a specific Experimental Example.

EXPERIMENTAL EXAMPLE

A glass substrate having a diameter of 30 cm and a thickness of 1.2 mmwas fixed to a substrate holder disposed in a bell jar of a vacuum filmformation device. Then, on the peripheral edge portion of the substratein the form of a disk, a mask having a projection portion having anouter diameter of 40 cm, an inner diameter of 29 cm and a thickness of 5mm was disposed. An inclined surface of the projection portion wasinclined at an angle of 45 degrees with respect to the face on which themask was disposed.

Then, a dielectric material layer 80 nm thick was formed on thesubstrate in a sputtering manner by using a dielectric materialcomprising ZnS as a target. In such a case, the inert gas pressure(sputtering pressure) was 0.04 Pa. Argon was used as the inert gas. Onthe thus formed dielectric material film, a recording film 90 nm thickcomprising TbFeCo was formed by a sputtering process. The inert gaspressure used herein was 0.6 Pa.

Then, on the thus formed recording film, a protection film 100 nm thickcomprising ZnS was formed by a sputtering process. The inert gaspressure used herein was 1.3 Pa.

When the outer peripheral side face of the thus prepared opticalrecording disk according to the present invention was observed by usinga scanning electron microscope (SEM), it was confirmed that the sideface of the recording film was completely covered with the protectionfilm. Further, the corrosion resistance of the above optical disk wasevaluated by comparing the corrosion resistance thereof with that of anoptical recording disk prepared according to a conventional productionprocess, by use of a test under high temperature and high humidityconditions. As a result, it was confirmed that the corrosion resistanceof the optical recording disk according to the present invention hadremarkably been improved, as compared with that of the conventionaloptical recording disk.

In the above specific Example, a photomagnetic recording disk of asingle side recording type is described as an example. However, thepresent invention is also applicable to a photomagnetic recording diskof a so called dual side recording type wherein a pair of plate memberscomprising a substrate and a recording film disposed thereon are bondedto each other so that the recording surfaces thereof are disposedopposite to each other. In addition, as a matter of course, the presentinvention is also applicable to an optical recording disk of anotherrecording type such as pit formation recording type, phase changerecording type and color change recording type.

The present invention provides an optical recording disk comprising alight transmissive substrate, a recording film disposed on the substratedirectly or through an intermediate layer and a protection film disposedon the recording film, the protection film comprises a dielectricmaterial and the entirety of the upper flat surface and the side surfaceof the recording film is integrally covered with the protection film. Asa result, in the optical recording disk according to the presentinvention, a substance capable of causing the corrosion thereof isprevented from entering the side face of the recording film, whereby thecorrosion resistance of the optical recording disk is remarkablyimproved.

The present invention also provides a process for producing an opticalrecording disk, which comprises: disposing, on a peripheral edge portionof a disk substrate, a mask in the form of a ring which has a projectionportion over the entirety of the inner peripheral portion of the ring;forming a recording film on the substrate by use of a sputteringprocess; and forming a dielectric material protection film by use of asputtering process under a pressure of an inert gas which is higher thanthat used at the time of the formation of the recording film. For thisreason, in the recording disk according to the present invention, theupper flat surface and the entirety of the side surface of the recordingfilm is integrally covered with the dielectric material protection film,whereby the corrosion resistance of the optical recording disk isremarkably improved.

What is claimed is:
 1. An optical recording disk comprising:a lighttransmissive substrate, a recording film disposed on the substratedirectly or through an intermediate layer, and a protection filmdisposed on the recording film, wherein an entire upper flat surface anda side surface of the recording film are integrally covered with thedielectric material protection film and said dielectric materialprotection film comprises a material selected from the group consistingof ZnS, SiN_(x), AlN, AlON, SiO, SiO₂, and CaF₂.
 2. An optical recordingdisk according to claim 1, wherein the recording film comprises a metalmaterial.
 3. An optical recording disk according to claim 1, wherein therecording film is laminated on the substrate so that it does not cover aperipheral edge portion of a flat surface of the substrate.
 4. Anoptical recording disk according to claim 1, wherein the intermediatelayer comprises a thin film consisting of a dielectric material.
 5. Anoptical recording disk according to claim 1, wherein the recording filmand the protection film have been formed by use of a sputtering process.